1. Field
The present general inventive concept relates to a regulator, and more particularly, to a negative feedback amplification system such as a low-dropout (LDO) voltage regulator.
2. Description of the Related Art
Low-dropout (LDO) voltage regulators are used to generate a stable voltage in devices such as cellular phones, wireless phones, pagers, personal digital assistants (PDAs), portable personal computers (PCs), camcorders and digital cameras, which are portable and can be operated by batteries. An LDO voltage regulator is characterized by an LDO voltage, i.e., a minimum difference between an unregulated input voltage, such as a voltage received from a battery or a transformer, and a regulated (or stable) output voltage. The LDO voltage regulator minimizes a dropout voltage so that portable devices can operate for a long time with a single battery voltage. Accordingly, the LDO voltage regulator alleviates a headroom condition and increases power efficiency as compared to a linear regulator with a high dropout voltage. Demand on LDO voltage regulators increases in direct proportion to demand on portable devices.
An LDO voltage regulator requires a capacitor installed at an outside portion of a chip to stabilize an output. However, since there are no standard guidelines regarding a capacitance level of an external capacitor used to stabilize an output of the LDO voltage regulator, capacitors having various values of 0.1 to 2 μF are used by different manufacturing companies. Accordingly, when LDO voltage regulators are designed, output stability (i.e., a phase margin) is compromised in order to satisfy the range of external capacitors.